1. Field of the Invention
The present invention relates to a catalytic metal article, and in more specific embodiments a catalytic metal plate and related methods of preparation and use. The article of present invention is useful for the treatment of gases to reduce contaminants contained therein.
2. Discussion of Related Art
The exhaust gases of internal combustion engines, including small engines, are known to contain pollutants such as hydrocarbons, carbon monoxide and nitrogen oxides (NOx) that foul the air.
Small internal combustion engines, usually two-stroke and four-stroke spark ignition engines are used to provide power to a variety of machinery, e.g. gasoline-engine powered lawn mowers, chain saws, leaf blowers, string cutters, leaf blowers, motor scooters, motorcycles, mopeds and the like. Such engines provide a severe environment for a catalytic exhaust treatment apparatus. This is because in small engines, the exhaust gas contains a high concentration of unburned fuel and unconsumed oxygen. A catalyst member can be mounted downstream of the engine inside another structure such as a muffler, as described in commonly assigned U.S. Ser. No. 08/682,247, herein incorporated by reference.
Additionally, the vibrational force in a two-stroke engine can be three or four times that of a four-stroke engine. For example, vibrational accelerations of 70 G to 90 G (G=gravitational acceleration) at 150 hertz (Hz) have been reported for small engines. The harsh vibration and exhaust gas temperature conditions associated with small engines lead to several modes of failure in the exhaust gas catalytic treatment apparatus, including failure of the mounting structure by which a catalyst member is secured in the apparatus and consequential damage or destruction of the catalyst member due to the mechanical vibration and to flow fluctuation of the exhaust gas under high temperature conditions. The catalyst member usually comprises a ceramic-like carrier member that has a plurality of fine parallel gas flow passages extending therethrough (sometimes referred to as a “honeycomb”) and which is typically made of, e.g., cordierite, mullite, etc., on which a catalytic material is coated. A typical carrier member has cells spaced 2.54 thick. The ceramic-like material is subject to cracking and pulverization by excessive vibration. While ceramic and metal monolithic honeycomb catalysts are known to be used in small engine applications, it is desirable to have an alternative design which avoids the fatigue.
Catalysts useful in small engine applications are described in U.S. Ser. No. 08/682,247, hereby incorporated by reference. Briefly such catalysts comprise one or more platinum group metal compounds or complexes which can be on a suitable support material. The term “compound”, as in “platinum group metal compound” means any compound, complex, or the like of a catalytic component which, upon calcination or use of the catalyst, decomposes or otherwise converts to a catalytically active form, which is often an oxide or metal. Various compounds or complexes of one or more catalytic components may be dissolved or suspended in any liquid which will wet or impregnate the support material.
Suitable support materials include refractory oxides such as alumina, silica, titania, silica-alumina, aluminosilicats, aluminum-zirconium oxide,, aluminum-chromium oxide, etc. Such materials are preferably used in their high surface area forms. For example, gamma-alumina is preferred over alpha-alumina. It is known to stabilize high surface area support materials by impregnating the material with a stabilizer species.
The catalytic materials are typically used in particulate form with particles in the micron-sized range, e.g., 10 to 20 microns in diameter, so that they can be formed into a slurry and applied as a washcoat on a carrier member. Suitable carrier members may be employed, such as a honeycomb-type carrier of the type having a plurality of fine, parallel gas-flow passages extending therethrough from an inlet or an outlet face of the carrier so that the passages are open to fluid-flow therethrough. Such honeycomb-type carrier may be made of any suitable refractory material such as cordierite, cordierite-alpha-alumina, silicon nitride, zirconium mullite, spodumene, alumina-silica magnesia, zirconium silicate, sillimanite, magnesium silicates, zirconium oxide, petallite, alpha-alumina and aluminosilicates. Alternatively, a honeycomb-type carrier may be made of a refractory metal such as a stainless steel or other suitable iron-based, corrosion-resistant alloys which can contain aluminum. The coater carrier is disposed in a canister suited to protect the catalyst member and to facilitate establishment of a gas flow path through the catalyst member, as is known in the art.
Three-way conversion catalysts (TWC) have utility in a number of fields including the treatment of exhaust from internal combustion engines, such as automobile and other gasoline-fueled engines. Catalytic converters containing a TWC catalyst can be located in the exhaust gas line of internal combustion engines. The catalysts promote the oxidation by oxygen in the exhaust gas of the unburned hydrocarbons and carbon monoxide and the reduction of nitrogen oxides to nitrogen.
Known TWC catalysts which exhibit good activity and long life comprise one or more platinum group metals (e.g., platinum or palladium, rhodium, ruthenium and iridium) located upon a high surface area, refractory oxide support, e.g., a high surface area alumina coating. The support is carried on a suitable carrier or substrate such as a monolithic carrier comprising a refractory ceramic or metal honeycomb structure, or refractory particles such as spheres or short, extruded segments of a suitable refractory material.
U.S. Pat. No. 4,134,860 relates to the manufacture of catalyst structures. The catalyst composition can contain platinum group metals, base metals, rare earth metals and refractory, such as alumina support. The composition can be deposited on a relatively inert carrier such as a honeycomb.
High surface area alumina support materials, also referred to as “gamma alumina” or “activated alumina”, typically exhibit a BET surface area in excess of 60 square meters per gram (“m2/g”) often up to about 200 m2/g or more. Such activated alumina is usually a mixture of the gamma and delta phases of alumina, but may also contain substantial amounts of eta, kappa and theta alumina phases. It is known to utilize refractory metal oxides other than activated alumina as a support for at least some of the catalytic components in a given catalyst. For example, bulk ceria, zirconia, alpha alumina and other materials are known for such use. Although many of these materials suffer from the disadvantage of having a considerably lower BET surface area than activated alumina, that disadvantage tends to be offset by a greater durability of the resulting catalyst.
It is a known expedient in the art to stabilize alumina supports against such thermal degradation by the use of materials such as zirconia, titania, alkaline earth metal oxides such as baria, calcia or strontia or rare earth metal oxides, such as ceria, lanthana and mixtures of two or more rare earth metal oxides. For example, see C. D. Keith, et al. U.S. Pat. No. 4,171,288.
Bulk cerium oxide (ceria) is disclosed to provide an excellent refractory oxide support for platinum group metals other than rhodium. U.S. Pat. No. 4,714,694 of C. Z. Wan, et al., discloses aluminum-stabilized bulk ceria, to serve as a refractory oxide support for platinum group metal components impregnated thereon. The use of bulk ceria as a catalyst support for platinum group metal catalysts other than rhodium, is also disclosed in U.S. Pat. No. 4,727,052 of C. Z. Wan, et al. and in U.S. Pat. No. 4,708,946 of Ohata, et al.
U.S. Pat. No. 4,808,564 discloses a catalyst which comprises oxides of lanthanum and cerium in which the molar fraction of lanthanum atoms to total rare earth atoms is 0.05 to 0.20 and the ratio of the number of the total rare earth atoms to the number of aluminum atoms is 0.05 to 0.25.
U.S. Pat. No. 4,438,219 discloses a stable alumina supported catalyst for use on a substrate. The stabilizing material is disclosed to be one of several compounds including those derived from barium, silicon, rare earth metals, alkali and alkaline earth metals, boron, thorium, hafnium and zirconium.
U.S. Pat. Nos. 4,294,726, 4,476,246, 4,591,578 and 4,591,580 disclose three-way catalyst compositions comprising alumina, ceria, an alkali metal oxide promoter and noble metals. U.S. Pat. Nos. 3,993,572 and 4,157,316 represent attempts to improve the catalyst efficiency of Pt/Rh based TWC systems by incorporating a variety of metal oxides, e.g., rare earth metal oxides such as ceria and base metal oxides such as nickel oxides. U.S. Pat. No. 4,591,518 discloses a catalyst comprising an alumina support with components deposited thereon consisting essentially of a lanthana component, ceria, an alkali metal oxide and a platinum group metal. U.S. Pat. No. 4,591,580 discloses an alumina supported platinum group metal catalyst. The support is sequentially modified to include support stabilization by lanthana or lanthana rich rare earth oxides, double promotion by ceria and alkali metal oxides and optionally nickel oxide. Palladium containing catalyst compositions e.g. U.S. Pat. No. 4,624,940 have been found useful for high temperature applications.
U.S. Pat. Nos. 3,956,188 and 4,021,185 disclose a catalyst composition having (a) a catalytically active, calcined composite of alumina, a rare earth metal oxide and a metal oxide selected from the group consisting of an oxide of chromium, tungsten, a group IVB metal and mixtures thereof and (b) a catalytically effective amount of a platinum group metal added thereto after calcination of said composite. The rare earth metals include cerium, lanthanum and neodymium.
U.S. Pat. No. 4,780,447 discloses a catalyst which is capable of controlling HC, CO and NOx as well as H2S in emissions from the tailpipe of catalytic converter equipped automobiles. The use of the oxides of nickel and/or iron is disclosed as an H2S gettering compound.
U.S. Pat. No. 4,965,243 discloses a method to improve thermal stability of a TWC catalyst containing precious metals by incorporating a barium compound and a zirconium compound together with ceria and alumina.
J01210032 (and AU-615721) discloses a catalytic composition comprising palladium, rhodium, active alumina, a cerium compound, a strontium compound and a zirconium compound. These patents suggest the utility of alkaline earth metals in combination with ceria, and zirconia to form a thermally stable alumina supported palladium containing washcoat.
U.S. Pat. Nos. 4,624,940 and 5,057,483 disclose compositions including ceria-zirconia containing particles. The '483 patent discloses that neodymium and/or yttrium can be added to the ceria-zirconia composite to modify the resultant oxide properties as desired. U.S. Pat. No. 4,504,598 discloses a process for producing a high temperature resistant TWC catalyst. The process includes forming an aqueous slurry of particles of gamma or other activated alumina and impregnating the alumina with soluble salts of selected metals including cerium, zirconium, at least one of iron and nickel and at least one of platinum, palladium and rhodium and, optionally, at least one of neodymium, lanthanum, and praseodymium.
U.S. Pat. Nos. 3,787,560, 3,676,370, 3,552,913, 3,545,917, 3,524,721 and 3,899,444 all disclose the use of neodymium oxide for use in reducing nitric oxide in exhaust gases of internal combustion engines. U.S. Pat. No. 3,899,444 discloses that rare earth metals of the lanthanide series are useful with alumina to form an activated stabilized catalyst support when calcined at elevated temperatures. Such rare earth metals are disclosed to include lanthanum, cerium, praseodymium, neodymium and others.
TWC catalyst systems comprising a carrier and two or more layers of refractory oxide are disclosed. One of the purposes of using catalysts having two or more layers is to isolate constituents of compositions in different layers to prevent interaction of the catalysts. Recent disclosures regarding catalysts comprising two or more layers are included in U.S. Ser. No. 08/645,985 and in European Patent Application Nos. 95/00235 and 95/35152. Two layer catalyst structures are disclosed in Japanese Patent Publication No. 145381/1975, Japanese Patent Publication No. 127649/1984, Japanese Patent Publication No. 19036/1985, Japanese Patent Publication No. 232253/1985, Japanese Kokai 71538/87, Japanese Patent Publication No. 105240/1982, Japanese Patent Publication No. 31828/1985, U.S. Pat. No. 4,806,519, JP88-240947, J63-205141A, J63-077544A and J63-007895A.
Japanese Patent Publication No. 52530/1984 discloses a catalyst having a first porous carrier layer composed of an inorganic support and a heat-resistant noble metal-type catalyst deposited on the surface of the support and a second heat-resistant non-porous granular carrier layer having deposited thereon a noble metal-type catalyst, said second carrier layer being formed on the surface of the first carrier layer and having resistance to the catalyst poison.
U.S. Pat. No. 4,587,231 discloses a method of producing a monolithic three-way catalyst for the purification of exhaust gases. First, a mixed oxide coating is provided to a monolithic carrier by treating the carrier with a coating slip in which an active alumina powder containing cerium oxide is dispersed together with a ceria powder and then baking the treated carrier. Next platinum, rhodium and/or palladium are deposited on the oxide coating by a thermal decomposition. Optionally, a zirconia powder may be added to the coating slip.
U.S. Pat. No. 4,923,842 discloses a catalytic composition for treating exhaust gases comprising a first support having dispersed thereon at least one oxygen storage component and at least one noble metal component, and having dispersed immediately thereon an overlayer comprising lanthanum oxide and optionally a second support. The layer of catalyst is separate from the lanthanum oxide. The noble metal can include platinum, palladium, rhodium, ruthenium and iridium. The oxygen storage component can include the oxide of a metal from the group consisting of iron, nickel, cobalt and the rare earths. Illustrative of these are cerium, lanthanum, neodymium, praseodymium, etc.
U.S. Pat. No. 5,057,483, referred to above, discloses a catalyst composition suitable for three-way conversion of internal combustion engine, e.g., automobile gasoline engine, exhaust gases and includes a catalytic material disposed in two discrete coats on a carrier. The first coat includes a stabilized alumina support on which a first platinum catalytic component is dispersed. The first coat also includes bulk ceria, and may also include bulk iron oxide, a metal oxide (such as bulk nickel oxide) which is effective for the suppression of hydrogen sulfide emissions, and one or both of baria and zirconia dispersed throughout as a thermal stabilizer. The second coat, which may comprise a top coat overlying the first coat, contains a co-formed (e.g., co-precipitated) rare earth oxide-zirconia support on which a first rhodium catalytic component is dispersed, and a second activated alumina support having a second platinum catalytic component dispersed thereon. The second coat may also include a second rhodium catalytic component, and optionally, a third platinum catalytic component, dispersed as an activated alumina support.
Emission control by retrofitting small engines such as those used on motorcycles with catalytic converters is disclosed in references such as Li-Kung Hwang, Pan-Hsiang Hsieh, James Wang, Wen-Bin Wang, Industrial Technology Research, Institute R.O.C., Small Engine Technology Conference, Volume II, Dec. 1-3, 1993, Pisa, Italy, pages 1009-1016. This reference discloses a wide range of motorcycle models retrofitted with catalytic converters to demonstrate the emission control strategy. The catalytic converters used had substrates which included ceramic and metallic substrates including a tube type substrate.